Why does an LED bulb cause a light failure warning?

The car measures the current each bulb draws, and an LED draws much less than the bulb it replaces, so the car reads it as burned out. Bulbs made for cars with bulb monitoring avoid it.

Does the warning go away by itself after I change the bulb?

Usually yes, once the lights are switched on again with a working bulb. The fault stays in the module's memory until it's cleared.

BMW light failure warning

BMWs check their exterior lamps electrically: the module that powers the lights measures the current each bulb draws. A lamp that draws nothing (a blown bulb) or the wrong amount (some LED replacements) shows a light failure warning naming the lamp.

The module stores the fault too, with the lamp's name, so the exact lamp can be read even when the message is gone.

Usual causes

A blown bulb.
An LED replacement bulb that draws too little current for the bulb check.
A corroded socket or connector, often in the tail lights or the trunk lid.
Wiring that breaks where it bends, at the trunk lid or tailgate hinge.

What to do

Check the lamp the warning names; replace the bulb if it's out.
Use the original type of bulb, or an LED bulb made for cars with bulb monitoring.
If the bulb is good, read the fault in the lights module or footwell module: it names the lamp, and the common light faults have their own pages with what to check.

General guidance from how BMWs work, not a diagnosis of your car: the fault the module stored, with its details, tells you more.

The fault codes behind it

Lights Module fault codes 145 codes · E60, E61, E63, E64, E65, E66, …
Driver's side footwell module fault codes 256 codes · E60, E61, E63, E64, E70, E71, …
Light check module fault codes 23 codes · E31

Reading the fault

AutoLingo for BMW reads the fault behind the light from the module that stored it, in plain English and with its details, and clears it after the repair, with BMW's own diagnostic protocols: a generic OBD2 code reader only reaches the engine's emissions faults. See what it does on your BMW.

Questions

Why does an LED bulb cause a light failure warning?: The car measures the current each bulb draws, and an LED draws much less than the bulb it replaces, so the car reads it as burned out. Bulbs made for cars with bulb monitoring avoid it.
Does the warning go away by itself after I change the bulb?: Usually yes, once the lights are switched on again with a working bulb. The fault stays in the module's memory until it's cleared.

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